I didn't say "large", I said "significant". Does a warrior with a season 3 weapon hit harder than a warrior with a season 2 weapon? Yes, he certainly does.
In a warrior+druid vs warrior+druid mirror match, could the ~30 extra top end damage make a difference in the game? Sure it could. Is it enough to give a player a slight edge in an otherwise equal match? Sure. Can you overcome the gear difference with superior skill, of course you can.
I still believe that the queue times for 2v2 is a bigger barrier to get a decent rating than any gear gap you could have, but it isn't something that can be totally ignored.
I don't think that rewarding "top" players with better items so that they get a statistical advantage over people with less skill is a good model to promote everyone to participate in the arena. You are better off giving out cosmetic rewards that do not directly impact game play. There is a lot that can be done to reward those with better rank, and I understand the desire to stand out from the crowd and be recognized for your accomplishments, but I don't think Blizzard wants to create a "haves and have-nots" split when it comes to pvp gear.